EP1994371B1 - Flowmeter for determining a flow direction - Google Patents

Description

The present invention relates to a flow measuring device for determining a flow direction of a fluid. The flow measuring device in this case has a measuring element with at least two optical waveguides and at least one adjacent to the optical waveguides electrical heating element, a control unit and an evaluation unit. Furthermore, the invention relates to a method for determining a flow direction of a fluid and to an electrical machine with the flow measuring device.

In electric machines of all power classes, but in particular with higher power, a considerable heat is developed, which is dissipated in terms of improved machine efficiency and / or longer life by means of cooling measures. For example, air-cooled machines such as generators or motors, in particular with powers below 300 MVA, are known in which cooling takes place by means of a comparatively large air flow. This air flow can in particular be conducted through a line system comprising numerous flow channels (cf., for example, US Pat DE 42 42 132 A1 or the EP 0 853 370 A1 ). It can be pressed through the stator of the machine, for example, through the flow channels of the duct system air from outside to inside. At the same time, however, air is sucked in by the rotor of the machine and pressed from the inside to the outside in the opposite direction by the stator. If both air streams interfere unfavorably, there will be a flow arrest within the piping system and thus, possibly, a local overheating and damage to the machine.

From the document C.Jewart et al., "X-probe flow sensor using self-powered active fiber Bragg gratings", Sensors and Actuators A 127 (2006), 63-68 An arrangement is known in by means of a cross of two fiber Bragg gratings a flow velocity is determined, wherein the optical waveguides are heated with the fiber Bragg gratings by light passed through.

From the GB 2 079 470 A For example, one way to determine the flow characteristics of a fluid through a liquid-permeable solid is known in which a heating element causes local heating of the solid and fluid and at other locations around the heating element the temperature is measured.

In the WO 2004/042326 A2 a flow measuring device is provided for determining a flow velocity of a fluid flowing around a measuring element of the flow measuring device, such as a gas flow, with an optical waveguide having a plurality of fiber Bragg gratings and at least one electrical heating element arranged adjacently to the conductor. Hereby, the flow velocity along the longitudinal extension of the measuring element can be determined from the influence of an electromagnetic wave fed into the optical waveguide by the temperature of the conductor. The optical waveguide can be heated by the electric heating element with constant application of heat, whereby a temperature distribution in the longitudinal extent corresponding to the local flow velocity results on the measuring element. This flow measuring device is thus suitable for determining a multiplicity of local flow velocities with only one single measuring element. Determining the direction in which the fluid flows relative to the measuring element, however, is not possible.

The present invention is therefore based on the object to provide a flow measuring device and a method with which the flow direction of a fluid can be determined, and to provide an electrical machine in which the flow direction of a cooling fluid can be monitored.

To achieve the object, a flow measuring device according to the features of independent claim 1 is given.

• ein von dem Fluid umströmbares Messelement mit mindestens zwei Lichtwellenleitern und mindestens einem zu den Lichtwellenleitern benachbart angeordneten elektrischen Heizelement, wobei
  • die Lichtwellenleiter über jeweils einen vom mindestens einen Heizelementen zu den jeweiligen Lichtwellenleitern gerichteten Wärmestrom mit Wärme beaufschlagbar ist,
  • die Richtungen der Wärmeströme zumindest anteilig entgegengesetzt sind,
  • die einzelnen Wärmeströme unterschiedlich stark mit der Strömungsrichtung des Fluids korreliert sind, und
  • wenigstens eine in die Lichtwellenleiter einkoppelbare elektromagnetische Welle entsprechend der jeweiligen Temperatur der Lichtwellenleiter beeinflussbar ist,
• eine Steuerungseinheit, mit welcher dem zumindest einen Heizelement elektrischen Leistung zuführbar ist, und
• eine Auswerteeinheit, mit welcher die von den einzelnen Wärmeströmen ausgehende Temperaturbeeinflussung der mindestens einen elektromagnetischen Welle auswertbar und die Strömungsrichtung des Fluids bestimmbar ist.

The flow measuring device according to the invention is a flow measuring device for determining a flow direction of a fluid, comprising

• one of the fluid flow around the measuring element with at least two optical waveguides and at least one adjacent to the optical waveguides electrical heating element, wherein
  • the optical waveguides can be acted upon by heat in each case via a heat flow directed by the at least one heating elements to the respective optical waveguides,
  • the directions of the heat flows are at least partially opposite,
  • the individual heat flows are correlated to different degrees with the flow direction of the fluid, and
  • at least one can be coupled into the optical waveguide electromagnetic wave corresponding to the respective temperature of the optical waveguide can be influenced,
• a control unit with which the at least one heating element electrical power is supplied, and
• an evaluation unit with which the temperature influence of the at least one electromagnetic wave emanating from the individual heat flows can be evaluated and the flow direction of the fluid can be determined.

The measuring element, which is arranged in its longitudinal extent preferably perpendicular to the flow direction of the fluid in this, has over the circumference of its cross-section, which is in particular circular, different local flow conditions. Thus, the heat transfer across the surface of the measuring element does not take place uniformly over the circumference of the cross section due to the spatially different flow velocities of the fluid. For this reason, a different heat flow in the direction of the optical waveguides, which are dependent on the position of the optical waveguides in the measuring element, is established in the measuring element for constant application of power to the at least one heating element. Depending on the arrangement of the optical waveguides relative to the flow direction, different temperatures can thus be set at the respective location of the optical waveguide. From the determination of the corresponding temperature differences, it is finally possible to deduce the flow direction of the fluid flowing around the measuring element.

Advantageous embodiments of the flow measuring device according to the invention will become apparent from the dependent claims of claim 1.

Thus, it is favorable if the optical waveguides each comprise at least one fiber Bragg grating and the at least one electromagnetic wave which can be coupled into the optical waveguides can be influenced at the location of the at least two fiber Bragg gratings in accordance with the respective temperature of the optical waveguides. Such a sensor type is characterized by its special multiplexing capability, so that a sensor network can be realized in a simple manner. Another advantage of the fiber Bragg grating technology is the possibility of a practically punctiform, so a locally very narrow measurement. This makes it possible, if a higher, in particular spatially resolved measurement accuracy along the measuring element is required, to arrange a plurality of fiber Bragg gratings close to one another in the respective optical waveguides one after the other.

For better distinctness, the fiber Bragg gratings arranged in an optical waveguide preferably each have a different centroid wavelength. In each fiber Bragg grating, a portion determined by the respective center of gravity wavelength is reflected back by the at least one fed-in electromagnetic wave. The center of gravity wavelength changes with the influencing variable prevailing at the measuring location, here in particular the temperature of the optical waveguide. This change in the wavelength content (or wavelength spectrum) of the respective back-reflected part of the fed-in at least one electromagnetic wave will be used as a measure of the influencing variable to be detected. In principle, however, it is also possible to examine the transmitted part of the fed-in at least one electromagnetic wave for the change in the wavelength spectrum. To query the fiber Bragg gratings by means of the at least one electromagnetic wave, in particular a broadband light source, such as For example, an LED (light-emitting diode, engl .: L ight E mitting D iode) with a bandwidth of about 45 nm, an SLD (super luminescent diode, engl .: S uper L uminescence D iode) with a bandwidth of about 20 nm or a tunable laser with a bandwidth of about 100 nm, are used.

It is proposed that the measuring element is rod-shaped. Advantageously, the measuring element is easy to assemble and can be introduced, for example, through an opening in the flow channel. Furthermore, it can be achieved that a maintenance of the measuring element is made possible with low assembly costs. For this purpose, the corresponding fasteners are released and the measuring element pulled out through the opening. In addition, the measuring element can of course have any other shape. For example, the measuring element may be circular or designed as an Archimedean spiral

In a further embodiment, it is proposed that the measuring element is elastic. Thus, advantageously, the measuring element can be preformed at short notice depending on the application, whereby the number of different measuring element shapes can be reduced. Storage costs can be saved.

It is favorable if the at least one heating element is formed from metal. Thus, a uniform heating along the heating elements is ensured.

Furthermore, it is proposed that the at least one heating element is formed by a common electrically conductive coating of the optical waveguides, wherein the optical waveguides are in contact in the longitudinal direction. Thus, the design of the measuring element can be further simplified. The heating element can thus be connected in a simple manner in each case in one piece with the conductors which are in contact with one another, so that in addition to a cost-effective production, a protective function of the conductors can also be achieved by the heating elements. The conductive coating may be, for example be formed of a metal such as tungsten or of an alloy such as steel or the like.

It is further proposed that the at least one heating element has a constant specific electrical resistance. Thus, it can advantageously be achieved that the measuring element is uniformly exposed to heat over its longitudinal extent. Specific electrical resistance in the context of this application is to be understood as the electrical resistance per unit length.

In addition, it is proposed that the specific resistance in the operating temperature range is largely independent of temperature. It can thus be achieved that the respective heat supply directed by the at least one heating element in the direction of the optical waveguide is substantially independent of the current local temperature along the longitudinal extent of the measuring element. The measurement accuracy as well as the reliability of the measurement can be increased. For this purpose, the at least one heating element may be formed, for example, from a material such as constantan or the like.

In an advantageous development, it is proposed that the measuring element has a casing. The measuring element can thus be protected against chemical attack, for example. In addition, the sheath allows mechanical protection, for example during assembly.

It is further proposed that the sheath consists of a ceramic material. With the ceramic jacket can advantageously be formed a measuring element for a high temperature stress.

In addition, it is proposed that the sheath is formed by a metal sleeve. Thus, advantageously, the measuring element can be protected, for example against electrostatic charge by the metal sleeve is connected to a ground potential.

In addition, it is proposed that the sheath (8) at the same time having at least one heating element (6, 7). Components and costs can be further reduced.

To further achieve the object, a method according to the features of independent claim 12 is given.

• mindestens eine elektromagnetische Welle in mindestens zwei Lichtwellenleiter eines vom Fluid umströmten Messelements eingekoppelt wird,
• zumindest einem Heizelement des Messelements derart elektrischen Leistung zugeführt wird, dass
  • die Lichtwellenleiter von den Heizelementen mit Wärme beaufschlagt und
  • die mindestens eine elektromagnetische Welle in Abhängigkeit von der unterschiedlichen lokalen Temperatur in den zumindest zwei Lichtwellenleitern unterschiedlich stark beeinflusst wird,
• die unterschiedlichen Beeinflussungen der mindestens einen elektromagnetischen Welle ermittelt und daraus die Strömungsrichtung des Fluids senkrecht zur Längserstreckung des Messelements bestimmt wird.

The inventive method is a method for determining a flow direction of a fluid with a flow measuring device, wherein

• at least one electromagnetic wave is coupled into at least two optical waveguides of a measuring element surrounded by the fluid,
• at least one heating element of the measuring element is supplied in such an electric power that
  • the optical fibers from the heating elements with heat and
  • the at least one electromagnetic wave is influenced differently depending on the different local temperature in the at least two optical waveguides,
• determines the different influences of the at least one electromagnetic wave and from this the flow direction of the fluid is determined perpendicular to the longitudinal extent of the measuring element.

In the method according to the invention, the advantages explained above for the flow measuring device according to the invention result.

Thus, it is also advantageous if the optical waveguides each comprise at least one fiber Bragg grating and the at least one electromagnetic wave is influenced as a function of the different, local temperatures at the location of the respective at least one fiber Bragg grating.

In addition, it is proposed that the at least one electromagnetic wave is formed by at least one electromagnetic pulse. Advantageously, energy can be saved and the measurement accuracy can be increased. The electromagnetic pulse can be generated for example by a pulsed laser, which is coupled via suitable known coupling means in the optical waveguide.

It is also proposed that the measuring element is heated in its longitudinal extent by the at least one heating element. From a temperature variation along the measuring element due to the fluid flow can advantageously be determined, the flow velocity along the measuring element.

It is advantageous that the at least one heating element is acted upon by a constant electrical power. In particular, in the case of a resistance course which is constant over the longitudinal extension of the measuring element, a constant application of heat can thus be achieved in each case in accordance with Ohm's law. This can be done by means of direct current or alternating current. In particular, by varying the AC frequency, the heating effect of the at least one heating element can be influenced when the frequency moves within a range in which current displacement effects take effect.

In an advantageous development of the method according to the invention, it is proposed that a plurality of measurements be carried out with different power application. Thus, the measurement accuracy can be further increased.

It is also proposed that the fluid used is a gas, in particular air, or a liquid, in particular water or liquid nitrogen, for cooling an electrical machine, in particular a generator or a motor. The measuring element according to the flow measuring device according to the invention can cost to the physical and / or chemical requirements in the flow channel of a cooling device of the generator or of the engine. An accurate measurement of a flow distribution in the cross section of a flow channel can also be achieved.

• einem drehbar gelagerten Läufer,
• einem zugeordneten, ortsfesten Stator in einem Maschinengehäuse,
• einer Einrichtung zur Kühlung von Teilen mittels eines Fluids innerhalb des Maschinengehäuses, wobei die Kühleinrichtung ein Leitungssystem enthält, und
• einer erfindungsgemäßen Strömungsmessvorrichtung vorgeschlagen.

Further, to further solve the problem with the invention, an electric machine with

• a rotatably mounted runner,
• an associated, fixed stator in a machine housing,
• a device for cooling parts by means of a fluid within the machine housing, wherein the cooling device includes a conduit system, and
• proposed a flow measuring device according to the invention.

In this case, an arranged in a flow channel of the conduit system measuring element of the flow measuring device for measuring the flow direction of the fluid is provided in the flow channel.

In the case of the electric machine according to the invention, the advantages explained above for the flow measuring device according to the invention result.

With the flow measuring device according to the invention, an efficient cooling of the machine can be achieved by the flow direction of the cooling fluid, such as air, is monitored in the flow channels of the cooling device. An occurring flow arrest due to unfavorably superimposed flows can be detected early enough so that appropriate measures can be taken to prevent local overheating and damage to the machine. Thus, the reliability of an operation of the turbomachine can be increased.

It is proposed that the measuring element is arranged radially to the cross section of the flow channel. Advantageously, the flow direction can be determined as a function of the radius of the flow channel cross section with a plurality of successively arranged fiber Bragg gratings. Of course, a plurality of measuring elements can also be provided in the flow channel in order to be able to determine the direction of flow at different circumferential positions of the flow channel.

It is further proposed that a plurality of measuring elements are arranged axially spaced apart in the flow channel. Thus, advantageously axial changes in the flow direction can be detected and evaluated. It is also possible to use a plurality of differently shaped measuring elements in order to obtain the desired information about the course of the flow. For example, radial, rod-shaped measuring elements can be combined with measuring elements arranged along a circular line in the flow channel. In particular, it is proposed that the measuring elements are operated in accordance with the method according to the invention.

Figur 1

eine Seitenansicht eines Messelements der erfin- dungsgemäßen Strömungsmessvorrichtung in stabförmi- ger Ausführung mit einem Anschlussstecker an einem Ende,

Figur 2

einen Schnitt durch eine Ausgestaltung eines Mess- elements mit einem Heizleiter sowie zwei parallel dazu angeordneten Lichtwellenleitern,

Figur 3

einen Schnitt durch eine Ausgestaltung eines Mess- elements mit zwei Heizleitern sowie zwei parallel dazu angeordneten Lichtwellenleitern,

Figur 4

einen Schnitt durch eine Ausgestaltung eines Mess- elements mit einem Heizleiter sowie vier parallel dazu angeordneten Lichtwellenleitern,

Figur 5

einen Schnitt durch eine weitere Ausgestaltung eines Messelements mit einem zwei Lichtwellenleiter umgebenden Heizelement,

Figur 6

einen Schnitt durch eine Ausgestaltung eines Mess- elements mit zwei parallel angeordneten und von je- weils einem Heizelement umgebenden Lichtwellenlei- tern,

Figur 7

einen Schnitt durch eine weitere Ausgestaltung ei- nes Messelements mit einem direkt auf den Oberflä- chen zweier sich berührenden Lichtwellenleiter auf- gebrachten Heizelement,

Figur 8

eine Prinzipschaltbild einer Ausführungsform der erfindungsgemäßen Strömungsmessvorrichtung mit dem Messelement gemäß Figur 2,

Figur 9

eine Prinzipschaltbild einer Ausführungsform der erfindungsgemäßen Strömungsmessvorrichtung mit dem Messelement gemäß Figur 3

Figur 10

eine Prinzipschaltbild einer Ausführungsform der erfindungsgemäßen Strömungsmessvorrichtung mit dem Messelement gemäß Figur 4

Figur 11

eine Prinzipschaltbild einer Ausführungsform der erfindungsgemäßen Strömungsmessvorrichtung mit dem Messelement gemäß Figur 6

Figur 12

eine Prinzipschaltbild einer Ausführungsform der erfindungsgemäßen Strömungsmessvorrichtung mit dem Messelement gemäß Figur 5 oder 7

Figur 13

Querschnitt eines Strömungskanals einer Kühlein- richtung mit einem Messelement der erfindungsgemä- ßen Strömungsmessvorrichtung,

Figur 14

einen Schnitt durch einen Generator mit mehreren Messelementen der erfindungsgemäßen Strömungsmess- vorrichtung.

Preferred, but by no means limiting embodiments of the invention will now be explained in more detail with reference to the drawing. For clarity, the drawing is not drawn to scale, and certain aspects are shown in schematic form. In detail, the show

FIG. 1

3 a side view of a measuring element of the flow measuring device according to the invention in a rod-shaped design with a connection plug at one end,

FIG. 2

1 a section through an embodiment of a measuring element with a heating conductor and two optical waveguides arranged parallel thereto,

FIG. 3

a section through an embodiment of a measuring element with two heating conductors and two parallel optical waveguides,

FIG. 4

3 shows a section through an embodiment of a measuring element with a heating conductor and four optical waveguides arranged parallel thereto, FIG.

FIG. 5

a section through a further embodiment of a measuring element with a heating element surrounding two optical waveguide,

FIG. 6

3 a section through an embodiment of a measuring element with two light waveguides arranged in parallel and surrounded by a respective heating element,

FIG. 7

3 a section through a further embodiment of a measuring element with a heating element applied directly to the surface of two contacting optical waveguides,

FIG. 8

a schematic diagram of an embodiment of the flow measuring device according to the invention with the measuring element according to FIG. 2 .

FIG. 9

a schematic diagram of an embodiment of the flow measuring device according to the invention with the measuring element according to FIG. 3

FIG. 10

a schematic diagram of an embodiment of the flow measuring device according to the invention with the measuring element according to FIG. 4

FIG. 11

a schematic diagram of an embodiment of the flow measuring device according to the invention with the measuring element according to FIG. 6

FIG. 12

a schematic diagram of an embodiment of the flow measuring device according to the invention with the measuring element according to FIG. 5 or 7

FIG. 13

Cross section of a flow channel of a cooling device with a measuring element of the flow measuring device according to the invention,

FIG. 14

a section through a generator with a plurality of measuring elements of the flow measuring device according to the invention.

FIG. 1 shows a side view of a measuring element 1a, 1b, 1c, 2, 3 or 31 of the flow measuring device according to the invention with a plug-in connection 15 attached to one end of the measuring element 1a, 1b, 1c, 2, 3 or 31 for connecting the measuring element 1a, 1b, 1c, 2, 3 or 31 to a control unit 20 and an evaluation unit 23 (see FIG FIGS. 8 to 12 and FIG. 14 ). The measuring element 1a, 1b, 1c, 2, 3 or 31 is rod-shaped. In addition, the measuring element 1a, 1b, 1c, 2, 3 or 31 can be made elastic, so that the geometric shape can be adapted to the given requirements.

In the FIGS. 2 to 13 In each case, a coordinate system 80 is associated with an x, y and z axis for a better overview. For the sake of simplicity and not limitation, it is assumed that the fluid 22 to be examined flows in the x-direction. The fluid 22 flowing in the x direction is indicated by arrows pointing in the x direction. The fluid 22, which flows in the x direction and strikes the measuring element 1a, 1b, 1c, 2, 3 or 31 extending in the y direction, flows around the latter. The fluid flow is in particular a turbulent flow. Different flow velocities are set on the surface 9 of the measuring element 1a, 1b, 1c, 2, 3 or 31. The length of the arrows indicates the amount of fluid velocity at the location shown. While the velocities are highest at that part of the measuring element surface 9 which is directed substantially in the direction of flow, it is lowest at that part of the measuring element surface 9 which points substantially in the flow direction. The heat transfer through the measuring element surface 9 takes place inhomogeneous depending on the local flow velocity. Thus, the heat transfer at that part of the measuring element surface 9, which is directed substantially opposite to the flow direction, greater than at that part of the measuring element surface 9, which has substantially in the flow direction. Is the measuring element 1a, 1b, 1c, 2, 3 or 31, the at least one heating element 5, 6 or 7, for example, in the center of the cross-sectional area of the measuring element 1a, 1b, 1c, 2, 3 or 31, at least with respect of its cross section in a thermal equilibrium, while it is acted upon by means of the at least one heating element 5, 6 or 7 with heat, an optical waveguide 4a arranged at or closer to that part of the measuring element surface 9, which is directed substantially in the direction of flow, becomes a lower one Have temperature, as an at or closer to that part of the measuring element surface 9, which faces substantially in the flow direction, arranged optical waveguide 4b. The optical waveguide 4a arranged at or closer to that part of the measuring element surface 9 which is directed essentially in the direction of flow is exposed to a lower heat flow 10a from the direction of the at least one heating element 5, 6 or 7 than at or closer to that part of the measuring element surface 9, which points substantially in the flow direction, arranged optical waveguide 4b. The heat flow associated with this optical waveguide 4b is indicated by 10b. The arrows pointing from the at least one heating element 5, 6 or 7 in the direction of the respective optical waveguides 4a, 4b indicate the corresponding heat flow 10a, 10b, the amount of which is reflected in the respective arrow length.

FIG. 2, FIG. 3 and FIG. 4 show three embodiments of a measuring element 1a, 1b and 1c of the flow measuring device according to the invention. According to the embodiment in FIG. 2 are two optical waveguides 4a, 4b and an interposed heating element 5 embedded in a ceramic material in the measuring element 1a included. According to the embodiment in FIG. 3 are two optical waveguides 4a, 4b and two interposed heating elements 5 embedded in the ceramic material in the measuring element 1b. In the respective FIGS. 2 and 3 For example, an optical waveguide 4a is arranged close to that part of the measuring element surface 9 which is directed substantially in the direction of flow, while the other optical waveguide 4b is positioned close to that part of the measuring element surface 9 which is directed substantially in the flow direction. The one Heating element 5 in FIG. 2 and both heating elements 5 in FIG. 3 are on an axis of symmetry 30 of the measuring element 1a and 1b, which simultaneously represents the mirror axis with respect to both optical fibers 4a, 4b, arranged such that their respective distances to the two optical fibers 4a, 4b correspond to each other. According to the embodiment in FIG. 4 are four optical waveguides 4a, 4b and an interposed heating elements 5 embedded in the ceramic material contained in the measuring element 1c. The four optical waveguides 4a, 4b are arranged in pairs near that part of the measuring element surface 9 which is directed substantially in the direction of flow or near that part of the measuring element surface 9 which is directed substantially in the direction of flow. The heating element 5 is arranged on an axis of symmetry 30 of the measuring element 1c, which simultaneously represents the mirror axis with respect to the optical waveguide pairs 4a, 4b, such that their distances from the respective optical waveguides 4a, 4b correspond to one another. The optical waveguides 4a, 4b are for example glass or plastic fibers. The at least one heating element 5 and the optical waveguides 4a, 4b are embedded in a ceramic body, in particular a cylindrical body 16, which in turn is surrounded by a passivating jacket 8. The one (cf. Figures 2 and 4 ) or the two (cf. FIG. 3 ) Heating elements 5 are formed for example as heating wires. In one embodiment, the sheath 8 can also be designed to be electrically conductive from a metal (cf. FIGS. 8 and 10 ).

FIG. 5 shows a further embodiment of a measuring element 2 of the flow measuring device according to the invention with two optical waveguides 4a and 4b, which are surrounded by a ceramic material consisting in particular cylindrical body 16. An optical waveguide 4a is arranged close to that part of the measuring element surface 9 which is directed substantially in the direction of flow, while the other optical waveguide 4b is located close to that part of the measuring element surface 9 which is essentially in the flow direction is directed, is positioned. Around the ceramic body 16, a heating element 6 is arranged such that it surrounds the measuring element 2. In particular, the heating element 6 simultaneously forms a sleeve-shaped casing 8 of the measuring element 2.

FIG. 6 FIG. 2 illustrates another embodiment of a measuring element 31 of the flow measuring device according to the invention with two optical waveguides 4a and 4b. Each optical waveguide 4a, 4b is surrounded by a corresponding heating element 6a, 6b or 7a, 7b in the form of a sleeve 6a, 6b or a coating 7a, 7b. The heating elements 6a, 6b or 7a, 7b are in turn surrounded by a ceramic material consisting in particular cylindrical body 16. An optical waveguide 4a with associated heating element 6a or 7a are arranged close to that part of the measuring element surface 9 which is directed substantially in the direction of flow, while the other optical waveguide 4b with associated heating element 6b or 7b near that part of the measuring element surface 9, which is substantially in Direction of flow is directed, are positioned. The ceramic body 16 itself is in turn surrounded by a sleeve-shaped passivating jacket 8 of the measuring element 31.

In FIG. 7 is a section through a measuring element 3 of the flow measuring device according to the invention, wherein two adjacent optical fibers 4a, 4b are vapor-deposited with a metal layers 7a, 7b, which also represents a heating element 7 of the measuring element 3. The metal layer 7 forms a common jacket 8 of the optical fibers 4a, 4b. This embodiment is characterized by an elasticity, so that the measuring element 3 can be adjusted as needed in its spatial extent. In addition, the measuring element 3 is distinguished by a particularly simple production method, in which the optical waveguide pair 4a, 4b is coated in a coating process of a conventional, known type with a suitable electrically conductive material. The embodiment is characterized further by from that they have a particularly low heat capacity compared to the embodiments of the measuring element 1a, 1b, 1c, 2 or 31 according to the FIGS. 1 to 6 and thus reacts faster to changing flow conditions.

The heating elements 5, 6 and 7 used in the aforementioned embodiments are preferably formed of a metal or of a metal alloy. Depending on the physical and / or chemical stress, for example steel, copper, aluminum, bronze, constantan or the like can be used. For high temperature applications, for example in the flow channel of a gas turbine, a coating with a metal such as tungsten or the like is preferable. For applications at low temperatures in a chemically aggressive environment, for example, conductive polymers can be used. In the embodiments illustrated here, the material of the heating elements 5, 6 and 7 each have a constant electrical resistance. In particular, the resistance in the operating temperature range is largely independent of the temperature. Applying the heating element 5, 6 and 7 with a constant current or with an alternating current with a constant effective value thus leads to a uniform over the length of the heating elements 5, 6 and 7 power supply, so that the corresponding heating element 5, 6 or 7 on the Longitudinal extent of the respective measuring element 1a, 1b, 1c, 2, 3 or 31 is applied uniformly with heat.

The FIGS. 8 to 12 show exemplary embodiments of the flow measuring device according to the invention in block diagrams. The flow measuring device in FIG. 8 comprises the measuring element 1a according to FIG. 2 , the flow measuring device in FIG. 9 comprises the measuring element 1b according to FIG. 3 , the flow measuring device in FIG. 10 includes the measuring element 1c according to FIG. 4 , the flow measuring device in FIG. 11 includes the measuring element 31 according to FIG. 6 and the flow measuring device in FIG. 12 includes the measuring element 2 or 3 according to FIG. 5 respectively. FIG. 7 , All mentioned embodiments the flow measuring device according to the invention further comprise a control unit 20 and an evaluation unit 23. The respective measuring element 1a, 1b, 1c, 2, 3 or 31 extends in its longitudinal axis in the y-direction. The measuring element 2 or 3 of the flow measuring device according to the FIG. 12 is at its respective ends with its heating element 6 or 7 electrically connected to the control unit 20 and at one of the two ends optically connected to the evaluation unit 23. In this case, the two optical waveguides 4a and 4b are connected in common to the evaluation unit 23 via a respective optical connecting fiber 25a, 25b. The measuring element 1a, 1b, 1c or 31 of the flow measuring device according to the FIGS. 8 to 11 is electrically connected at one end to the control unit 20 and optically connected to the evaluation unit 23, while the other end of the measuring element 1 is freely available. Hereby, a particularly simple assembly and / or handling of the measuring element 1a, 1b, 1c or 31 can be achieved. One of the optical waveguides 4a, 4b of the measuring element 1a, 1b, 1c or 31 is connected via an optical connecting fiber 25 to the evaluation unit 23, wherein the optical waveguides 4a, 4b are interconnected in series. The individual optical fibers 4a, 4b can also be analogous to FIG. 12 be individually connected to the evaluation unit 23 without having to connect to each other.

The control unit 20 has an electrical energy source 21. The power source 21 having two terminals is connected to the heating elements 5, 6 or 7 according to the embodiments such that the heating element 5, 6 or 7 is supplied with electric power and generates heat. The electrical energy source 21 is in particular a current source, via which a constant direct current can be predetermined.

The measuring element 1a, 1b, 1c, 2, 3 or 31 flows around the fluid 22, wherein the fluid flow along the longitudinal extension of the measuring element 1a, 1b, 1c, 2, 3 or 31 may have a different flow velocity indicated through the arrows of different lengths. The flow direction of the fluid 22 has, for simplicity, in the x-direction, as already stated above. For a measurement of the flow direction of the fluid 22, the heating element 5, 6 or 7 of the measuring element 1a, 1b, 1c, 2, 3 and 31 is supplied with electrical power, so that this heats up. The heating process should last at least until a thermal equilibrium has been established in the measuring element 1a, 1b, 1c, 2, 3 or 31. He can also be chosen shorter.

By means of the evaluation unit 23, which has a light source, a detector and an analyzing means, light, in the form of a continuous laser beam or in the form of laser pulses, is transmitted via the optical connecting fiber 25 into the optical waveguides 4a, 4b of the measuring element 1a, 1b, 1c, 2 , 3 or 31 coupled and analyzed backscattered light with the analysis means. For the measurement, the effect is exploited that an electromagnetic wave, which is coupled into an optical waveguide 4a, 4b, is scattered when passing through the optical waveguide 4a, 4b. A part of the scattered light is scattered in the opposite direction, so that it can be detected at the entrance of the optical waveguide 4a, 4b. Due to the temperature dependence of this scattering effect can be close to the temperature of the optical waveguide 4a, 4b. The backscattered light signal consists of different components that are different in terms of measurement requirements. For example, the backscattered signal contains a Raman scattered portion. With the fiber Bragg grating technology, a higher spatial resolution can be achieved compared to the Raman technology, which is preferable in particular for the use of temperature measurement in machines.

The laser light is generated in known manner with prior art devices. Depending on the temperature, part of the laser light in the optical waveguides 4a, 4b is scattered back by fiber Bragg gratings 13. This backscattered Light signal is supplied via the optical connecting fiber 25 of the evaluation unit 23, which determines therefrom the temperature at the location of the fiber Bragg gratings 13 in the optical waveguide 4.

By means of the evaluation unit 23, the corresponding individual optical waveguides 4a, 4b associated temperatures within the measuring element 1a, 1b, 1c, 2, 3 or 31 are determined. Depending on the relative position of the respective optical waveguide 4a, 4b, different temperatures occur at the location of the optical waveguides 4a, 4b in the measuring element 1, 2 or 3 in a flowing fluid 22 with directed flow. By means of the evaluation unit 23, the different temperatures are compared with each other, for example by subtraction in one of the evaluation unit 23 associated computer unit, and from which determines the flow direction of the fluid 22.

Does the measuring element 1a, 1b, 1c, 2, 3 or 31 a plurality of fiber Bragg gratings 13 along the optical waveguides 4a, 4b, as in the embodiments in FIG. 8 to FIG. 12 indicated, the flow velocity with the flow velocity distribution of the fluid 22 can be determined from the temperature distribution along the measuring element 1a, 1b, 1c, 2, 3 or 31.

In the embodiment of the flow measuring device according to the invention FIG. 8 For example, the measuring element 1a has a heating element 5 designed, for example, as a heating wire. The energy source 21 is connected to the heating element 5 by one connection and to the electrically conductive jacket 8 of the measuring element 1a by the other connection. The heating element 5 is also connected to the electrically conductive sheath 8 at the opposite end of the measuring element 1a.

In the embodiment of the flow measuring device according to the invention FIG. 9 the measuring element 1b has two parallel For example, designed as heating wires heating elements 5, wherein the two heating wires are connected together at one end of the measuring element 1b with an electrical connection conductor. At the other end of the measuring element 1b while one of the two heating elements 5 are connected to one terminal of the power source 21 and the other heating element 5 to the other terminal of the power source 21. Likewise, at one end of the measuring element 1 b, the two parallel optical waveguides 4 a, 4 b are interconnected with an optical connecting fiber, while at the other end measuring element 1 b only one of the two optical waveguides 4 a, 4 b is connected to the evaluation unit 23 via an optical connecting fiber 25.

In the embodiment of the flow measuring device according to the invention FIG. 10 the measuring element 1 has a total of four parallel optical waveguides 4a, 4b. Between the optical waveguides designed as a heating wire heating elements 5 is arranged. The energy source 21 is connected to the heating element 5 with one connection and to the electrically conductive jacket 8 of the measuring element 1c via the other connection. The heating element 5 is also connected to the electrically conductive sheath 8 at the opposite end of the measuring element 1c. The four optical waveguides 4a, 4b are connected to one another in series by means of optical connecting fibers at the measuring element ends, so that only one of the optical waveguides 4a, 4b is connected directly to the evaluation unit 23. The use of such a measuring element 1c with numerous optical waveguides 4a, 4b, which are arranged, for example, in a circle around the heating element 5 arranged in the cross-sectional center of the measuring element 1c, allows an even more accurate determination of the flow direction of the fluid 22.

In the embodiment of the flow measuring device according to the invention FIG. 11 For example, the measuring element 31 has two parallel heating elements 5 formed, for example, as electrically conductive sleeves or coatings, the two on one end of the measuring element 31 are joined together. At the other end of the measuring element 31 while one of the two heating elements 5 are connected to one terminal of the power source 21 and the other heating element 5 to the other terminal of the power source 21. Likewise, at one end of the measuring element 1 b, the two parallel optical waveguides 4 a, 4 b are interconnected with an optical connecting fiber, while at the other end measuring element 1 b only one of the two optical waveguides 4 a, 4 b is connected to the evaluation unit 23 via an optical connecting fiber 25.

But it is also conceivable, analogous to FIG. 8 and FIG. 10 , the two heating elements 5 off FIG. 9 and FIG. 11 connected together at one end together with the casing 8, which is designed to be electrically conductive in this case, so that the energy source 21 at the other end of the measuring element 1b and 31 can also be connected to the casing 8. In this exemplary embodiment, not shown, both heating elements 5 must be connectable together with one and the same connection of the energy source 21.

In the embodiment of the flow measuring device according to the invention FIG. 12 is a connection of the power source 21 at one end of the measuring element 2 or 3 with the electrically conductive sleeve 8 (FIG. FIG. 5 ) or as an electrically conductive coating ( FIG. 7 ) formed heating element 6 or 7 connected. The second terminal of the power source 21 is connected at the other end of the measuring element 2 or 3 by means of an electrical line to the heating element 6 or 7.

FIG. 9 shows a circular cross section of a flow channel 14 through which a fluid 22 flows in the x direction. The flow channel 14 is provided as an example with two with respect to the flow channel cross-section radially arranged measuring elements 1a, 1b, 1c, 2, 3 or 31. The two measuring elements 1a, 1b, 1c, 2, 3 or 31 are connected via an electrical connection line 26 with the control unit 20 and an optical connection fiber 25 is connected to the evaluation unit 23.

In FIG. 10 a generator is shown schematically as an electrical machine. The generator has a stationary stator 19 fixedly connected to a housing 28 and a rotor 18 movably mounted on a rotor shaft 17. The generator is cooled by means of a cooling device with, for example, air as cooling fluid 22. For this purpose, the cooling device has two fans 27, which conduct the cooling air 22 through the generator by means of a line system. For this purpose, the line system has numerous flow channels, in particular also in the stator 19. The cooling air 22 is conducted in the illustrated embodiment from outside to inside in the direction of rotor 18 through the stator 19 and further transported by a gap between stator 19 and rotor 18 gap to the outside. At the same time, however, air can be sucked in by the rotor of the generator 22 and pressed from the inside to the outside in the opposite direction by the stator 19. If both air streams interfere unfavorably, there will be a flow arrest within the piping system and thus, possibly, a local overheating and damage to the generator. To avoid this, the flow direction in the flow channels is monitored by means of the flow measuring device according to the invention. In this embodiment, two flow channels, each with a measuring element 1a, 1b, 1c, 2, 3 or 31 of the flow measuring device according to the invention are provided as an example at two points of the generator. Both measuring elements 1a, 1b, 1c, 2, 3 or 31 are connected to the associated control unit 20 and evaluation unit 23. In the case of irregularities in the flow of cooling air, it is therefore possible to react promptly and to take appropriate protective measures.

The use of the flow measuring device according to the invention in an air-cooled generator is used here only as an example. It is also possible to use the flow measuring device according to the invention in electrical machines with H ₂ gas a noble gas or any gas other than fluid 22 are cooled. As cooling fluid 22 may also be a cooling liquid, such as water or even in cryogenic cooling, a liquid noble gas or liquid nitrogen may be provided.

The flow measuring device according to the invention can also be used in a turbine, such as a steam turbine or a gas turbine. Thus, by means of the flow measuring device according to the invention, flow directions can be measured, in particular in turbulent flow regions in the associated cooling air system, in the associated compressor, at the associated compressor inlet and / or in the corresponding exhaust gas flow.

The exemplary embodiments illustrated in the figures merely serve to explain the invention and are not restrictive of it. Thus, in particular the type of the measuring element 1a, 1b, 1c, 2, 3 or 31, in particular its geometric shape, vary without departing from the scope of the invention. In addition, of course, several elements can be interconnected in order to investigate certain changes in the flow direction in more detail.

Claims (21)

1. Flowmeter for determining a flow direction of a fluid (22), having

   - a measurement element (1a, 1b, 1c, 2, 3, 31) around which the fluid (22) can flow and having at least two optical waveguides (4a, 4b), each of which comprises at least one fibre Bragg grating (13a, 13b), and having at least one electrical heating element (5, 6, 7), which is arranged adjacent to the optical waveguides (4), in which

   - heat can be applied to the optical waveguides (4a, 4b) via a respective heat flow (10a, 10b), which is directed from the at least one heating element (5, 6, 7) to the respective optical waveguides (4a, 4b),

   - at least a proportion of the directions of the heat flows (10a, 10b) is in opposite directions,

   - the individual heat flows (10a, 10b) are correlated to different extents with the flow direction of the fluid (22),
   and

   - at least one electromagnetic wave, which can be injected into the optical waveguides (4a, 4b), can be influenced in accordance with the respective temperature of the optical waveguides (4a, 4b) at the location of the at least two fibre Bragg gratings (13a, 13b),

   - a control unit by means of which electrical power can be supplied to the at least one heating element (5, 6, 7),
   and

   - an evaluation unit (23), by means of which it is possible to evaluate the temperature influence, originating from the individual heat flows, on the at least one electromagnetic wave, and to determine the flow direction of the fluid (22).
2. Flowmeter according to Claim 1, characterized in that the measurement element (1a, 1b, 1c, 2, 3, 31) is in the form of a rod.
3. Flowmeter according to Claim 1 or 2, characterized in that the measurement element (1a, 1b, 1c, 2, 3, 31) is elastic.
4. Flowmeter according to one of Claims 1 to 3, characterized in that the at least one heating element (5, 6, 7) is formed from metal.
5. Flowmeter according to one of Claims 1 to 4, characterized in that the at least one heating element (7) is formed by a common electrically conductive coating on the optical waveguides (4a, 4b), with the optical waveguides being in contact in the longitudinal direction.
6. Flowmeter according to one of Claims 1 to 5, characterized in that the at least one heating element (5, 6, 7) has a constant electrical resistivity.
7. Flowmeter according to Claim 6, characterized in that the resistivity in the operating temperature range is largely independent of temperature.
8. Flowmeter according to one of Claims 1 to 5, characterized by a sheath (8) for the measurement element (1a, 1b, 1c, 2, 3, 31).
9. Flowmeter according to Claim 8, characterized in that the sheath (8) is composed of a ceramic material.
10. Flowmeter according to Claim 8, characterized in that the sheath (8) is formed by a metal sleeve.
11. Flowmeter according to Claim 10, characterized in that the sheath (8) also has the at least one heating element (6, 7).
12. Method for determining a flow direction of a fluid (22) by means of a flowmeter, in which

    - at least one electromagnetic wave is injected into at least two optical waveguides (4a, 4b) of a measurement element (1a, 1b, 1c, 2, 3, 31) around which the fluid (22) flows, the optical waveguides (4a, 4b) each comprising at least one fibre Bragg grating (13a, 13b)

    - at least one heating element (5, 6, 7) for the measurement element (1a, 1b, 1c, 2, 3, 31) is supplied with electrical power such that

    - heat is applied by the heating elements (5, 6, 7) to the optical waveguides (4a, 4b), and

    - the at least one electromagnetic wave is influenced to a different extent as a function of the different local temperature in the at least two optical waveguides (4a, 4b) at the location of the respective at least one fibre Bragg grating (13a, 13b),

    - the different influences on the at least one electromagnetic wave are determined and the flow direction of the fluid (22) at right angles to the longitudinal extent of the measurement element (1a, 1b, 1c, 2, 3, 31) is determined from this.
13. Method according to Claim 11 or 12, characterized in that the at least one electromagnetic wave is formed by at least one electromagnetic pulse.
14. Method according to one of Claims 11 to 13, characterized in that the measurement element (1a, 1b, 1c, 2, 3, 31) is heated in its longitudinal extent by the at least one heating element (5, 6, 7).
15. Method according to one of Claims 11 to 14, characterized in that the at least one heating element (5, 6, 7) has a constant electrical power applied to it.
16. Method according to one of Claims 11 to 15, characterized in that a plurality of measurements are carried out with a different power applied.
17. Method according to one of Claims 11 to 16, characterized in that a gas or a liquid is used as the fluid (22) for cooling an electrical machine (9), in particular a generator or a motor.
18. Electrical machine having

    - a rotor (18) which is mounted such that it can rotate,

    - an associated fixed-position stator (19) in a machine housing (28),

    - a device for cooling parts by means of a fluid (22) within the machine housing (28), with the cooling device (27, 14) containing a line system,
    and

    - a flowmeter according to one of Claims 1 to 11,
    with a measurement element (1a, 1b, 1c, 2, 3, 31) which is arranged in a flow channel (14) of the line system, of the flowmeter being provided in order to measure the flow direction of the fluid (22) in the flow channel (14).
19. Electrical machine according to Claim 18, characterized in that the measurement element (1a, 1b, 1c, 2, 3, 31) is arranged radially with respect to the cross section of the flow channel (14).
20. Electrical machine according to one of Claims 18 or 19, characterized in that a plurality of measurement elements (1a, 1b, 1c, 2, 3, 31) are arranged at a distance from one another axially in the flow channel (14).
21. Method according to one of Claims 12 to 17, characterized in that the flow direction of a fluid (22) in a cooling line system of an electrical machine is determined according to one of Claims 18 to 20.

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